1. Field of the Invention
The present invention relates to vortex cancellation for aircraft in general, and in particular to a wingtip vortex device for induced drag reduction and vortex cancellation at the wingtips of aircraft.
2. Related Art
Current wingtip vortex devices operate on the principle of self-cancellation of counter-rotating vortices generated in tandem. Typical vortex devices employ a propeller or related rotary device mounted at wingtips to produce vortex cancellation. Many studies of anti-swirl-producing propellers have been performed and documented.
Typically, a propeller is installed ahead of or behind the wingtip chord where, as a byproduct of thrust generation, the propeller generates swirl, while also weakening the wingtip vortex, to thereby reduce induced drag. However, since current propellers are designed to produce thrust efficiently, they are only marginally effective in producing counter-swirl. Such a deficiency was pointed out by Alexander Lippisch as reported by Snyder and Zumwalt in "Effects of Wingtip-Mounted Propellers on Wing Lift and Induced Drag", Journal of Aircraft, Vol. 6, No. 5, September-October 1969.
As a result, an impeller was disclosed as a more effective alternative. An impeller consists of an oval-oblong-shaped body having a multitude of slender fins on its periphery. The impeller can efficiently produce swirling flow. Snyder and Zumwalt achieved a 64-percent induced drag reduction with an impeller as described.
Nevertheless, although the impeller disclosed by Snyder and Zumwalt is quite efficient in producing swirling flow, it generates little or no thrust. Also, Snyder and Zumwalt do not provide information on the power needed to drive the impeller. Thus, a process which requires mechanical power (presumably from the propulsion system) to reduce drag has little technical merit.
Therefore, what is needed is an impeller device that limits or eliminates wingtip vortices by utilizing a "free" power source, such as the rotational energy of the wingtip vortex itself, to drive the impeller. What is also needed is a wind turbine device installed downstream of a wingtip of an aircraft to not only extract mechanical power from the vortex, but to reduce induced drag at the same time. What is additionally desired is a device that utilizes the power generated from the turbine device for driving aircraft subsystems.
Whatever the merits of the above mentioned systems and methods, they do not achieve the benefits of the present invention.